The present invention is directed to a universal patellar clamp.
In total knee replacement surgery, a prosthesis is provided in which one component is fastened to the distal end of the femur which has been resected and another component is fastened to the proximal end of the tibia which has been resected so that the two components will act together in permitting the leg to bend and straighten out. In performing such surgery, the patella is not normally replaced but rather is resurfaced such that the interior crown portion facing the condyles is cut and reamed to form a cavity in which a patellar prosthesis is implanted. The patellar prosthesis has a crown facing inwardly to engage the patellar or trochlear groove of the femoral component.
In preparing a patella for an implant, it is usually necessary to engage the patella with a clamp having a circular cross sectional configuration and, using the interior surface of the clamp as a guide, ream a cavity in the patella of sufficient size to receive the patellar implant intended to be used. Depending upon a number of factors including the size of the patient, the patellar implant could be one of a number of different sizes. As a result of this, it was, heretofore, necessary to have available a number of clamps each having a different diameter for guiding various size reamers. Typical prior art methods of forming a cavity for implanting a patellar prosthesis are shown and described in the following publications, which are incorporated herein by reference: Brochures entitled "The AMK Total knee System Design Rationale and Surgical Procedure" (page 25), DePuy, Division of Boehringer Mannheim Corporation, Warsaw, Ind., and "WHITESIDE ORTHOLOC.RTM. Modular KNEE SYSTEM", copyright 1989 by Dow Corning Wright, Arlington, Tenn. Copies of such references are herewith enclosed.
There has recently been introduced a new design of patellar prosthesis having a tapered surface on the side away from the crown. One such prosthesis is the subject matter of U.S. patent application Ser. No. 07/508,088, filed Oct. 18, 1990, by the applicant herein. The method for implanting such a patellar prosthesis is the subject-matter of my copending U.S. patent application Ser. No. 652,882 and the clamp of my present invention is well-suited for use with the method disclosed in such patent application; however, it should be understood that the apparatus of the present invention is not so limited and may be used with a wide variety of methods for implanting a patellar prosthesis. It has a significant advantage over the prior art for implanting a patellar prosthesis of a type in which one of a number of different sizes is to be used depending upon the patient in that the present invention provides a universally sized patellar clamp to guide the reamer. Accordingly, in utilizing the apparatus of the present invention, it is not necessary to have available a plurality of clamps of varying sizes.
To aid in the understanding of the apparatus of this invention, it is necessary to briefly summarize the surgical method disclosed and claimed in the U.S. patent application Ser. No. 652,882. The '882 invention provides a new method for preparing a human patella for implanting a patellar prosthesis therein and a new method for implanting a patellar prosthesis in a human patella. As is well-known in performing knee replacement surgery, the patella is everted and retained in a position permitting the surgeon to have access to the articular surface which is normally engaged in the intercondylar notch between the condyles. Under the '882 invention, with the patella so supported, the surgeon, using a saw or similar tool for performing osteotomy, removes the top portion of the articular surface, thus leaving a flat surface near the central portion of the patella. Desirably, only a small portion of the articular surface is removed in order to leave as much of the original patella intact as possible. Thus, as pointed out in the above-identified patent application, it is desirable that as little of the human patella be removed as possible.
Following removal of the top of the articular surface a threaded guidewire or pin is used to drill a passageway in the central portion of the patella at substantially right angles to the flat surface. Then, using the threaded guidewire which may be left in the passageway or a rod of similar size to that of the threaded guidewire positioned in said passageway, a cannulated reamer is placed over the threaded guidewire or other guide rod and, using such threaded guidewire or guide rod as a guide, the reamer is utilized to ream the patella thereby forming a cavity having a size and configuration suitable for receiving the patellar prosthesis. Following such reaming, the cavity is cleaned, bone cement placed therein and the patellar prosthesis implanted therein. If desired, the reaming could be performed in stages, initially using a reamer sized to form a relatively small cavity and thereafter using a reamer sized to form the cavity for receiving the patella prosthesis.